Metal oxide semiconductor (MOS) field-effect transistors with very thin gate dielectrics made from silicon dioxide may experience unacceptable gate leakage currents. Forming the gate dielectric from certain high-k dielectric materials, instead of silicon dioxide, can reduce gate leakage. When, however, a high-k dielectric film is initially formed, it may have a slightly imperfect molecular structure. To repair such a film, it may be necessary to anneal it at a relatively high temperature. In addition, annealing the high-k dielectric film improves transistor reliability.
Because conventional high-k dielectric layers may not be compatible with polysilicon, it may be desirable to use metal gate electrodes in devices that include high-k gate dielectrics. Metal gate electrodes provide high performance relative to polysilicon. Unfortunately, the metals or alloys used in metal gate electrodes cannot tolerate the high temperatures necessary to anneal the high-k dielectric film. As a result, because the metals or alloys desirable for high performance cannot withstand the high temperatures needed for reliability, conventional high-k dielectric metal gate transistors cannot provide both high performance and high reliability.
As such, there is a need for a method of making a semiconductor device that includes a metal gate electrode coupled with an annealed high-k dielectric layer. The high temperature anneal needs to be applied to the high-k dielectric layer without damaging any metal that may be used to make the gate electrode.